Walter E. Ellis, 50, was convicted last week after he pleaded no contest to charges of first-degree intentional homicide and first-degree murder, which carry a mandatory sentence of life in prison.

Judge Dennis Cimpl had the option of allowing the possibility of parole but declined. He sentenced Ellis to seven consecutive life sentences.

The sentencing brings a close to a killing spree that began in 1986. The subsequent investigations eventually led to a complete review of how the state maintains its DNA database.

All seven victims were strangled, either manually or with a rope or clothing tied around their necks. One was also stabbed.

Ellis was arrested in 2009 after police said his DNA matched semen samples found on six victims and a blood sample on a can of pepper spray found at the scene of the seventh slaying. Authorities have said they began to focus on Ellis after his name surfaced in connection with a number of unsolved homicides.

Ellis’ case exposed flaws in the state’s process for collecting DNA from convicted felons. Ellis’ DNA was missing from a state database even though he should have submitted a sample during an earlier prison stint. Authorities said Ellis had a fellow inmate submit a DNA sample in his place.

Police have said that if the sample had been taken at that time, they may have been able to track Ellis down before the last slaying, in 2007.

The discovery prompted a state audit, which found nearly 17,700 offender samples missing from the crime lab’s database.